Control devices are often provided in building control and other systems to control power that is applied to a load. In some cases, such control devices can be powered by transformers or the like, which are configured to delivers a voltage suitable for powering the control devices. Alternatively, or in addition, some control devices may be powered by a battery or the like. Because transformers and batteries can add expense and complexity to many systems, power stealing circuits are sometimes used.
Some control devices may include a “power stealing” circuit that steals power from an electrical signal that powers the load. The power stealing circuit can power the control device during normal operation. A difficulty that can be encountered in such systems is, when stealing power, the electrical signal that powers the load may be affected by the power stealing circuitry, causing unexpected or reduced performance and increased Electro-Magnetic Interference (EMI). Accordingly, there is a need for new and improved power stealing circuits for power control devices.